Chronic myelogenosus luekemia (CML) is characterized by increased formation of granulocytes and other blood forming elements which, with a median time of three years, is almost uniformly fatal. Conventional chemotherapeutic regimens for its initial chronic phase have failed to prevent transformation to acute leukemia or to significantly affect survival. Although bone marrow transplantation is effective treatment regimens for the chronic phase phase have to be designed. We previously demonstrated that gamma interferon (IFN-gamma) has potent supressive effects on hematopoiesis in vitro and provided evidence implicating it in the pathogenesis of the hemotopoietic suppression observed in a plastic anemia. Preliminary work has also demonstrated a similar suppressive effect of IFN-gamma on the in vitro hematopoietic colony formation in patients with CML. This evidence, coupled with the in vivo suppression of myelopoiesis observed in patients treated with recombinant IFN-gamma for other disorders, makes this agent particularly well suited to the treatment of CMA; preliminary studies support this. We have designed and received approval for a study of the treatment of patients with both the chronic phase and the accelerated phase (a transition phase from the chronic to the acute stages of the disease) with recombinant IFN-gamma. Patients in the chronic phase will be treated with continuous subcutaneous administration, for preliminary evidence would suggest that in order to be effective, maximum exposure time to IFN-gamma is needed. Patients in the accelerated phase will be treated with daily intramuscular administration. Several studies have already begun to study the biology of this unique disorder.